In recent years, a variety of technologies have been developed for electronically controllable beam shaping, for a variety of applications, such as electrically tunable lenses for camera or flash applications. Other configurations of beam shaping devices have been proposed for lighting applications, such as general illumination and vehicle lamps. Several of these technologies for controllable beam shaping have used liquid crystals, which are optically anisotropic. Optically anisotropic materials are said to be birefringent (or birefractive). Birefringence is an optical property of a material having a refractive index that depends on the polarization and propagation direction of light. In optics, the refractive index (or index of refraction) is a dimensionless number that describes how light propagates through that medium
Liquid crystal displays utilize liquid crystals to change the birefringence of polarized display in image display applications, but are generally unsuitable for illumination lighting. The liquid crystal material is sandwiched between an input polarizer and output polarizer to form controllable pixels of the display. Typically, liquid crystal displays incorporate a diffuser to spread unpolarized light emitted by a backlight before that unpolarized light enters the input polarizer to undergo polarization prior to entering the liquid crystal material. After passing through the liquid crystal material, the polarized light passes through an output polarizer to form a displayed image. Generally, a diffuser is not coupled to an output surface of the output polarizer because the diffuser would adversely affect quality of the displayed image by mixing the light forming the displayed image outputted by the controllable pixels.
Electrokinetics is a microfluidic phenomenon that refers to several different effects that occur in a heterogenous fluid that contains particles. The particles are solid, liquid, or gas on the scale of micrometers or nanometers. The source of the effects are the influence of an external force, such as an electrical charge, on the particles. Electrophoresis is a specific electrokinetic phenomenon in which an electric field moves the particles. Electrophoresis principles have been used in films for window timing to change the color or darkness/brightness of a window and in electronic-paper display (or e-reader) devices. An example color electrophoretic device for window tinting or e-readers utilizes electrophoresis to attract charged color particles to a top transparent electrode to spread color or to a bottom compact electrode to hide the colored particles in micro-pits, which are adjacent to the bottom compact electrode. In particular, the position of the particles relative to the electrodes and light may turn the pixel white, dark, or somewhere in between, including color state. However, such electrophoretic devices do not operate by changing the refractive index of the electrophoretic fluid to control birefringence, but rather merely bring the charged particles in and out of the field of view (e.g., like a window shutter).